Cytology is a branch of biology dealing with the study of the formation, structure, and function of cells. As applied in a laboratory setting, cytologists, cytotechnologists, and other medical professionals make medical diagnoses of a patient's condition based on visual examination of a specimen of the patient's cells. A typical cytological technique is a “pap smear” test, in which cells are scraped from a woman's cervix and analyzed in order to detect the presence of abnormal cells—a precursor to the onset of cervical cancer. Cytological techniques are also used to detect abnormal cells and disease in other parts of the human body.
Cytological techniques are widely employed because collection of cell samples for analysis is generally less invasive than traditional surgical pathological procedures such as biopsies, whereby a tissue specimen is excised from the patient using specialized biopsy needles having spring loaded translatable stylets, fixed cannulae, and the like. Cell samples may be obtained from the patient by a variety of techniques including, for example, by scraping or swabbing an area, or by using a needle to aspirate body fluids from the chest cavity, bladder, spinal canal, or other appropriate area. The cell samples are placed in solution and subsequently collected and transferred to a glass slide for viewing under magnification. Fixative and staining solutions may be applied to the cells on the glass slide for preserving the specimen for archival purposes and for facilitating examination.
It is generally desirable that the cells on the slide have a proper spatial distribution, so that individual cells can be examined. A monolayer of cells is typically preferred. Accordingly, preparing a specimen from a fluid sample containing many cells typically requires that the cells first be separated from each other by mechanical dispersion, fluidic shear, or other techniques so that a thin, monolayer of cells can be collected and deposited on the slide. In this manner, the cytotechnologist can more readily discern abnormal cells. The cells are also able to be counted to ensure that an adequate number of cells have been evaluated.
Certain methods and apparatus for generating a thin monolayer of cells on a biological slide advantageous for visual examination are disclosed in U.S. Pat. Nos. 5,143,627, 5,240,606, 5,269,918, and 5,282,978, the disclosures of which are expressly incorporated herein by reference.
Two commercially successful apparatus manufacturing in accordance with the teachings of one or more of these patents has been marketed as the ThinPrep™ 2000 and ThinPrep™ 3000 Processors (the “ThinPrep™ Processor”) by Cytyc Corporation, located in Boxborough, Mass. During this commercial process, a gynecologic sample is collected using a broom-type or cytobrush/spatula cervical sampling device. Then, the sampling device is rinsed into a vial containing PreservCyt® transport medium. The sample vial is then capped, labeled, and sent to a laboratory for slide preparation. At the laboratory, the vial is placed into the ThinPrep™ Processor, which under control of the instrument's microprocessor, performs the following procedures.
First, the ThinPrep™ Processor uses a portable sample collection device to disperse and collect cells from the liquid sample contained within the sample vial. The sample collection device comprises a disposable plastic filter cylinder, which is introduced by the ThinPrep™ Processor into the liquid sample, and a non-disposable filter plug, which the ThinPrep™ Processor uses to interface with the filter cylinder. The filter plug holds the filter cylinder in an air-tight connection to the ThinPrep™ Processor's pneumatic network for the purpose of collecting cells from the liquid sample. FIGS. 1A and 1B illustrate a conventional filter plug 10 used in connection with the ThinPrep™ Processor. The filter plug 10 is a reusable component that is inserted into a filter cylinder 12 that contains a membrane 14 at one end thereof. A seal is formed between the filter plug 10 and the inner surface of the filter cylinder 12 using an o-ring 16 that is located within a groove 18 of the filter plug 10. The o-ring 16 is compressed to form the sealing engagement with the filter cylinder 12. In order to obtain the cell samples, the ThinPrep™ Processor generates a negative pressure pulse that draws fluid through the filter plug 10 (in the direction of arrow A in FIG. 1B), and collects a thin, even layer of diagnostic cellular material on the filter membrane 14. The ThinPrep™ Processor constantly monitors the rate of flow through the sample collection device during the collection process to prevent the cellular presentation from being too scant or too dense. The ThinPrep™ Processor then generates a positive pressure pulse that deposits the cellular material on a glass slide. The slide is then analyzed to determine whether the sample is positive or negative for a specified disease.
In the filter plug 10 illustrated in FIGS. 1A and 1B, as the filter plug 10 is inserted into the filter cylinder 12, a compression force is immediately placed on the o-ring 16. While this compression force is ultimately needed for the proper seal between the filter plug 10 and the filter cylinder 12, the immediate frictional forces between the o-ring 16 and the interior of the filter cylinder 12 place extra burdens on the insertion and extraction force requirements for the filter plugs 10. In addition, the immediate frictional forces may cause the o-ring 16 to roll or twist, which may result in an incomplete seal being formed. The frictional engagement or rubbing contact between the o-ring 16 and the filter cylinder 12 in filter plugs 10 of the type illustrated in FIGS. 1A and 1B also cause wear on the o-ring 16 which may also result in an incomplete seal. A partial or incomplete seal is, of course, problematic because of the potential for cross-contamination between samples resulting from fluid and/or debris buildup on the filter plug 10.